Entwicklung neuer Schutz- und Kontaktierungsschichten für Hochtemperatur-Brennstoffzellen

Kiefer, Thomas

Dissertation / PhD Thesis/Book

Entwicklung neuer Schutz- und Kontaktierungsschichten für Hochtemperatur-Brennstoffzellen

Kiefer, T. (Corresponding author)FZJ*

2008
Forschungszentrum Jülich GmbH Zentralbibliothek, Verlag Jülich
ISBN: 978-3-89336-514-2

Jülich : Forschungszentrum Jülich GmbH Zentralbibliothek, Verlag, Schriften des Forschungszentrums Jülich : Energie & Umwelt / Energy & Environment 3, 138 S. (2008) = Bochum, Univ., Diss., 2007

Please use a persistent id in citations: http://hdl.handle.net/2128/3105 http://hdl.handle.net/2128/3054

Abstract: Iron-chromiumalloys (ferritic steels) forming a chromia oxide scale(Cr$_{2}$O$_{3}$) are promising materials as metallic interconnector of solid oxide fuel cells (SOFC). Typical operating temperatures of such fuel cells range between 600 and 800 °C. Chromia-containg oxide scales are necessary since they show sufficient electrical conductivity unlike alumina(Al$_{2}$O$_{3}$) or silica scales(SiO$_{2}$). However, one of the disadvantages of such alloys are volatile Cr(VI)species like CrO$_{3}$ and CrO$_{2}$(OH)$_{2}$. These volatile species arise under operating conditions of SOFC. The electrochemical reduction of these species forming solid Cr(III) oxides at the three phase boundary electrolyte / cathode / oxidant leads to a degradation of the cell performance. Such degradation is unacceptable in regard of long-term operation (> 40000 h). The use of protective coatings is necessary to assure a stable stack performance over long-time period. For protective coatings spinel structures in the ternary system Mn$_{2}$O$_{3}$ – CuO – Fe$_{2}$O$_{3}$ and Mn$_{2}$O$_{3}$ – Co$_{3}$O$_{4}$ – Fe$_{2}$O$_{3}$ are considered. Especially the nominal compositions CuMn$_{1.9}$Fe$_{0.1}$O$_{4}$, MnCo$_{2}$O$_{4}$ and MnCo$_{1.9}$Fe$_{0.1}$O$_{4}$ exhibit a high electrical conductivity and a fitting coefficient of thermal expansion to that of other components. Exposures under cathodic operating conditions are performed to evaluate protective coatings in terms of chromium retention, chemical stability and electrical performance. Forthis purpose the compositions of protective coatings mentioned above are applied within a simulated stack section (interconnector| protective/contact coating| cathode). The protective/contact coatings are applied on interconnector plates. This compound is pressed on a sintered cathode material. The fuel cell performance depends on the interaction between the protective coating and surrounding components. Because of this, three commercial ferritic steels namely Crofer22APU „ThyssenKrupp AG“(Germany), F17TNb „Imphy Ugine Precision (I.U.P.)“ (France) und IT-11„PlanseeSE“(Austria) and the cathode material(La$_{0.65}$Sr$_{0.3}$MnO$_{3-\delta}$ (LSM)and La$_{0.58}$Sr$_{0.4}$Co$_{0.2}$Fe$_{0.8}$O$_{3- \delta}$(LSCF)) are varied to investigate theinfluence of different interactions. The interaction between protective coating and steel canalso be a function of processing. Therefore wet chemical coatings are compared withthermally sprayed coatings. The thermally sprayed coatings are applied using an atmosphericplasma spraying process (APS). Chromium as well as iron can always be detected within the protective layer in case of a wet chemical process and a sub-sequent sintering process under atmospheric conditions. The elements migrate from the steel substrate into the protective coating. Due to the presence of these elements the properties of the protective coatings are changed. The electrical conductivity as well as the coefficient of thermal expansion deteriorate compared to the [...]

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